http://www.emedicine.com/EMERG/topic500.htm#target1: An explanation of the causes, pathophysiology, investigation and management of ARF.
http://www.nlm.nih.gov/medlineplus/ency/article/000501.htm: An encyclopaedic insight into ARF with many explanatory links.
http://www.nephrologychannel.com/arf/index.shtml: A simpler explanation of ARF aimed at patients.
http://www.aafp.org/afp/20000401/2077.html: Another site explaining ARF with some interesting pictures and algorithms.
Acute Renal Failure: Causes and Prognosis: A pdf copy of a chapter on ARF.